Known compounds having the same skeleton as the compound of the above-described formula (I) and also exhibiting a blood platelet aggregation inhibitory activity include a series of compounds disclosed in Japanese Patent Publication No. 23994/81 corresponding to U.S. Pat. No. 3,932,407 and U.S. Pat. No. 4,641,718.
However, among the above-described known compounds, those having excellent anti-platelet aggregation activity are all sparingly soluble in water and are not, therefore, suitable for parenteral administration. Further, these compounds are characterized by their potent hypotensive activity, and such a hypotensive activity rather exerts a harmful influence on the circulatory systems when applied in the therapy of thromboembolia making use of their platelet aggregation inhibitory activity.
Also, U.S. Pat. No. 4,256,748 discloses imidazo[2,1-b]quinazolin-2(3H)-ones which are useful for treating and prophylaxis of cardiac insufficiency and cardiac failure, but these compounds have a substituent such as an alkyl group at the 3-position of the imidazo[2,1-b]quinazolin skeleton and their activity is different from that of the compound of this invention.